Polyethylene polymers, blends thereof with other polymers, and articles made therefrom are generally known in the art. Many varieties of polyethylene polymers have been prepared over the years, including those made using high pressure free radical chemistry (LDPE), traditional linear low density polyethylene (LLDPE) typically made using Ziegler-Natta processes, and polyethylene made by metallocene or other catalysts. Generally, polyethylenes made by different processes have different molecular architectures and distribution characteristics giving rise to varying positives and negatives, depending on application or end-use.
One way to categorize polyethylene polymers is based on the presence, amount, and character of long-chain branching in the distribution of polymer molecules. Generally, long-chain branches are those branches longer than branches resulting from direct incorporation of monomer. Another feature of polyethylenes is the distribution of short chain branches. Some polyethylenes have a relatively uniform comonomer architecture. Thus, such polyethylenes have a comonomer content that is relatively constant over the distribution of molecular weights in the composition. In other words, such polyethylenes can be said to have a relatively low percentage of molecules having a comonomer content within 50% of the median total molar comonomer content. Others polyethylenes have a narrow distribution of comonomer incorporation as reflected by a relatively high percentage of molecules having a comonomer content within 50% of the median total molar comonomer content. In addition to the relative breadth in the distribution of the comonomer branches over the molecular weight range, polyethylenes can be differentiated based on the relative molecular regime into which the comonomer branches incorporate. Thus, in some polyethlyenes, the comonomer may be preferentially incorporated in lower molecular weight molecules. In others, the comonomer branches are more concentrated in higher molecular weight molecules. While each of these features is generally known, the particular combinations of these and other features that may lead to unique property combinations suitable for particular uses is difficult to predict.
Polyethylene having certain combinations of such properties that lead to improved properties and versatility in film applications is still needed to meet performance and application targets.